1. Field of the Invention
The invention relates to a display apparatus such as television receiver, view finder of a video camera, monitor for a terminal of a computer, or the like or to a display apparatus such as a projector having a light valve or the like. More particularly, the invention relates to method and apparatus for driving a liquid crystal display apparatus in which a liquid crystal has a memory performance in a liquid crystal device in which scanning signal lines and information signal lines are arranged in a matrix form and which is used to display video information by being driven by applying a scanning signal and an information signal to those signal lines, respectively.
2. Related Background Art
Hitherto, a refresh scanning type CRT is mainly used as a computer terminal display apparatus. A frame frequency of 60 Hz or higher is used to prevent the flickering of the screen. A non-interlace system is also used to improve the visibility of the moving display (movement using a mouse, an icon, or the like) of information in the screen. Therefore, as a display resolution rises, a high power is required and the size and costs of a drive control section also increase. In the television receiver, the interlace system is used, a field frequency is set to 60 Hz, and a frame frequency is set to 30 Hz for the purpose of convenience of the moving image display and simplicity of a drive control system.
In recent years, a flat panel display is highlighted because of inconvenience of the large size and high power of the CRT.
At present, there are several systems as a flat panel display. For example, there are a high time division system of a twisted nematic liquid crystal (STN), a system for a black and white display (NTN) as a modification of the STN, a plasma display system, and the like. All of those systems use the same system as that of the CRT as an image data transfer system. As a screen updating system, the non-interlace system having a frame frequency of 60 Hz is used. This is because since those display panels don't have a memory performance in terms of the display principle, a refresh cycle of a frequency that is equal to or higher than the frame frequency of 60 Hz or higher is needed to prevent the flickering. Even in a system (TFT, MIM, TFD, etc.) such that a switching transistor or a non-linear device is formed in each pixel of the twisted nematic liquid crystal, image information can be held within up to one frame. Therefore, a refresh cycle of 60 Hz or more is also necessary in a manner similar to each of the above systems.
On the other hand, since a display apparatus using a ferroelectric liquid crystal has a feature (memory performance) such that the image information which was once displayed can be held, a fairly larger screen and higher fineness than those of the above various kinds of display apparatuses can be realized. Since such a ferroelectric liquid crystal display apparatus is driven by a low frame frequency, however, in order to cope with the man-machine interface type display apparatus, a partial rewriting scanning (only the scanning line in which the image information was changed is scanned (driven)) system using the memory performance is necessary. With respect to such a partial rewriting scanning system, for instance, trials to realize it have been being made by the method of "low frame frequency driving (multi-interlace scanning) +partial rewriting scanning" to perform a display at a high resolution in a display apparatus having the memory performance which has been disclosed in Japanese Patent Laid-Open Application No. 63-285141, Japanese Patent Laid-Open Application No. 63-65494, or the like proposed by the present inventors et al. on the basis of the system proposed in the Official Gazette of U.S. Pat. No. 4,655,561 by Kamibe et. al.
In Japanese Patent Laid-Open Application No. 5-27716 or the like, there is disclosed the method of "Memory display" such that in the case where there is a change in image information, a partial rewriting is executed and, in the case where there is no change, no voltage is applied to a liquid crystal display device. By such a method, an electric power consumption is reduced and a durability is improved.
In the drive control method of the liquid crystal display device so far, as mentioned above, when there is a change in image information, the partial rewriting scanning is executed and, when there is no change, either one of the following processes is executed.
(1) The whole screen refresh scanning by the multi-interlace or the like is continued.
(2) The apply of the signal is stopped and the memory display is performed.
In the whole screen refresh scanning of (1), however, there is a case where when the same image is displayed for a long time, a picture quality deteriorates. In the memory display system of (2) which can improve such a drawback, since contrasts upon driving and upon memory display are different, there is a case where a flickering occurs when the driving means is switched.